1. Field of the Invention
The invention relates to hollow fiber membrane exchangers. While the invention is subject to a wide range of applications, it is especially suited for use in oxygenating blood and will be particularly described in that connection.
2. Description of the Related Art
During open heart surgery, natural cardiovascular activity is suspended, which causes the lungs to collapse. It is therefore necessary to simulate the function of the lungs, which replaces carbon dioxide in the blood with oxygen. Blood oxygenators serve this function. A typical hollow fiber blood oxygenator includes a bundle of hollow fibers extending through a blood chamber for conveying oxygen into the blood chamber and for removing carbon dioxide from the blood therein. Specifically, the fibers are constructed of a membrane material that acts as a boundary between extracorporeal blood flow and oxygen flow. As blood flows on the outside of the fibers and oxygen passes through the hollow fibers, a gas exchange occurs wherein oxygen passes through the fiber walls and into the blood and carbon dioxide passes, in the opposite direction, from the blood into the interior of the hollow fibers.
There are multiple and sometimes conflicting parameters that must be considered when designing a hollow fiber membrane exchanger. For example, the longer blood remains in contact with the fibers, the greater the amount of gas exchange that may occur. Thus, it may be desirable to design the oxygenator so that the length of the flow path of the blood relative to the hollow fibers is maximized to thereby maximize contact between blood and the hollow fibers. On the other hand, it is desirable to construct an exchanger that is as small and compact as possible. Thus, the desire to build a compact unit is somewhat constrained by blood flow path length requirements.
Biocompatibility is also a factor that must be considered in exchanger design. For example, membrane exchangers are typically manufactured from multiple components that are joined together with adhesives. However, in order to minimize the possibility of bioincompatibility between the blood and the materials that make up the exchanger, it is preferable to minimize the number of materials with which extracorporeal circulating blood comes into contact. Thus, while adhesives may be necessary, it is beneficial to limit the amount of adhesive that is located in the blood flow path.
Finally, gas exchange requirements, which are often dependent upon a particular use, also place constraints on the ultimate design of an exchanger. For example, adults typically have greater gas exchange requirements than children, and therefore require a larger membrane compartment. Therefore it is common for manufacturers to offer exchangers of varying sizes/each size being designed for a particular gas exchange requirement, and each size employing its own uniquely sized parts. However, this is not cost effective. From a cost efficiency perspective, it is easier to develop economies of scale if many of the same parts can be used regardless of the membrane size. Thus, it is preferable to provide a membrane exchanger that is constructed of as many standard parts as possible for use with membranes of varying sizes.